The present nonprovisional application claims priority under 35 USC 119 to Japanese Patent Application No. 2002-193360 filed on Jul. 2, 2002 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
This invention relates to an exhaust system for a small watercraft that is propeled with jet water jetted from a jet pump.
2. Description of Background Art
A personal watercraft is a watercraft wherein a jet pump is attached to a rear portion of a watercraft body and is driven by an engine to take in water from the bottom of the watercraft and jet the taken-in water rearwardly to propel the watercraft.
A personal watercraft is known as set forth in Japanese Patent Laid-Open No. Hei 10-212936 entitled xe2x80x9cExhaust System for a Personal Watercraft.xe2x80x9d Essential part of FIG. 1 of the Official Gazette for his patent is incorporated herein as FIG. 8 and a description is given below of the exhaust system for this personal watercraft.
FIG. 8 is a side elevational view showing the conventional small watercraft. The small watercraft 100 includes an engine 102 provided at a substantially central location of a watercraft body 101. A water muffler 104 is connected to the engine 102 by an exhaust pipe 103, and a substantially inverted U-shaped exhaust pipe 105 is provided for the water muffler 104.
The substantially inverted U-shaped exhaust pipe 105 is connected at one end thereof to the water muffler 104, and extends, at a substantially half portion 106 thereof adjacent the substantially inverted U-shaped exhaust pipe 105, upwardly once and then extends, at the remaining substantially half portion 107 thereof, downwardly such that it generally has a substantially U-shape.
With the substantially inverted U-shaped exhaust system, exhaust gas and cooling water having arrived at the inside of the water muffler 104 from the engine 102 side can be discharged to the outside through the U-shaped exhaust pipe 105.
However, since the cooling water and the exhaust gas in the water muffler 104 flow in a mixed state into the exhaust pipe 105, the cooling water flows through an overall sectional area in the inside of the exhaust pipe 105.
Where the cooling water flows through an overall sectional area in the inside of the exhaust pipe 105 in this manner, it is estimated that the cooling water may fill up the inside of the exhaust pipe 105 to disturb a flow of the exhaust gas.
Therefore, it is an object of the present invention to provide an exhaust system for a small watercraft wherein exhaust gas can flow smoothly.
In order to solve the subject described above, according to the present invention, an exhaust system for an engine incorporated in the small watercraft includes a water muffler wherein an exhaust pipe connected to the water muffler extends upwardly once and then extends downwardly in such a manner as to have a substantially U-shape and exhaust gas and cooling water in the water muffler are discharged to the outside through the U-shaped exhaust pipe. A spiral baffle plates is provided for spirally introducing the exhaust gas. The spiral baffle plates are provided on an inner face of the U-shaped exhaust pipe.
Since the spiral baffle plates are provided on the inner face of the exhaust pipe, a flow of exhaust gas can be converted into a spiral flow by the baffle plates. Consequently, centrifugal force acts upon cooling water having entering into the exhaust pipe together with the exhaust gas so that the cooling water can be drawn up to the inner face of the exhaust pipe.
Consequently, since the cooling water can flow along the inner face of the exhaust pipe while the exhaust gas flows along a central portion of the exhaust pipe, the cooling water and the exhaust gas can be separated from each other.
According to the present invention, the exhaust system for a small watercraft includes an on/off valve capable of opening and closing an outlet of the exhaust pipe that is provided at the outlet of the exhaust pipe.
The on/off valve is provided on the outlet side of the exhaust pipe such that the outlet of the exhaust pipe can be opened or closed with the on/off valve. Since the on/off valve is provided, admission of water into the exhaust pipe from the outlet side can be prevented.
Incidentally, where the on/off valve is provided on the outlet side of the exhaust pipe, it is considered that a support member that supports the on/off valve may cross the outlet of the exhaust pipe. In this instance, there is a possibility that, if cooling water and exhaust gas flow in a mixed state with each other in the exhaust pipe, then the cooling water may strike against the support member and may reside in the proximity of the outlet of the exhaust pipe. Therefore, it maybe considered that the residing cooling water may have a bad influence on the flow of the exhaust gas to disturb the flow of the exhaust gas.
Therefore, in the present invention, the exhaust system, is configured such that the cooling water flows along the inner face of the exhaust pipe while the exhaust gas flows along a central portion of the exhaust pipe to separate the cooling water and the exhaust gas each other. When the cooling water and the exhaust gas are separated from each other in this manner, the cooling water striking against the support member can be prevented from disturbing the flow of the exhaust gas.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.